The present invention generally relates to medical electrical leads; and, more specifically, to a bifurcated lead system designed for big-ventricular pacing and defibrillator from within two branches of a cardiac vein.
It has become common to provide electrical stimulation to a patient""s heart by positioning multiple medical electrical leads at various locations within the cardiac system. For example, a first lead may be positioned within the right atrium of the heart for pacing and sensing of the right atrium. A second lead may be positioned within the right ventricle for pacing and sensing of the right ventricle.
Several problems exist when multiple leads are positioned within the heart or associated vascular system. Generally, both leads will be introduced into the heart through a common location as through the superior venal cave. Movement of one lead with respect to the other lead at this common entry location may cause dislodgement of one or both of the leads. Additionally, if the leads are in close proximity to one another, relative movement of the leads causes the lead insulation to wear, and may result in lead failure.
One manner of addressing the above-described problems involves providing a single, bifurcated lead system. This type of lead system includes a first portion, or xe2x80x9cfingerxe2x80x9d, of the lead that that is generally adapted for placement in the right atrium. A second portion, or xe2x80x9cfingerxe2x80x9d, of the lead is designed to be advanced within the right ventricle. A lead system of this nature is described in commonly-assigned U.S. Pat. No. 4,643,201 to Stokes. Similarly, U.S. Pat. No. 5,769,881 to Schroeppel et al. describes a branch assembly that accommodates the selective use of one stylet to position first and second distal fingers of a lead within the right atrium and ventricle, respectively, of the heart. U.S. Pat. No. 5,628,779 to Bomnzin et al. disclose a bifurcated lead having a J-shaped finger locations at a proximal portion of the lead, and an oppositely-shaped distal curved portion. The two curves may be straightened by a stylet during lead deployment. Upon removal of the stylet the lead re-assumes a curved shape, allowing the J-shaped extension to protrude into the right atrial appendage while the distal end of the lead drapes through the tricuspid valve and into the right ventricular apex.
The above-discussed systems discuss lead systems for use in pacing within the right atrium and ventricle. Recently, it has become apparent that pacing in both ventricles can provide important benefits to patients. This is particularly true for patients suffering from heart failure. One investigation has shown that left ventricular pacing should be focused at the site of latest left ventricular activation to create synchronized contractions with right ventricular apical pacing. This location is typically the posterior or posteroinferior base for most patients with chronic LV dysfunction. (Leclercq C, et al. Acute hemodynamic effects of biventricular DDD pacing in patients with end-stage heart failure. J Am Coll Cardiol 1998; 32 (7):1825-31) Pacing electrodes may be implanted deep within the coronary sinus at the ostium of a lateral or posterolateral vein to pace from this location.
Current lead systems for performing big-ventricular pacing utilize two leads, each located within a respective ventricle. This results in some of the disadvantages discussed above. What is needed, therefore, is an improved system for performing big-ventricular pacing that may be used to re-synchronize contractions within the right and left ventricles. Ideally, the system would address the problems associated with multiple-lead pacing systems that are discussed above.
The present invention provides a left-sided big-furred medical electrical lead that is adapted to be implanted in the cardiac venous system. The inventive lead includes a bifurcated distal portion having first and second elongated members, or fingers. In one embodiment, the first elongated member, or thumb portion, is adapted to be positioned within the coronary sinus or great cardiac vein. This thumb is particularly adapted to be positioned within the coronary sinus near the ostium of the great cardiac vein in a posterolateral position along the base of the left ventricle. The second elongated member, or finger portion of the bifurcated distal tip, may be positioned within a branch vessel of the coronary sinus such as the posterior vein or middle cardiac vein.
According to one aspect of the inventive lead system, the thumb portion may carry at least one electrode for pacing and/or sensing, and may carry additional electrodes for multi-polar pacing applications. Portions of the pacing/sensing electrode may be insulated so that electrical stimulation is only delivered to myocardial tissue, and not to muscle or nerve tissue located posterior to the heart. The finger portion may carry a defibrillator electrode. Additional electrodes may be carried along the lead body for pacing and/or sensing.
In one embodiment of the bifurcated lead system, the finger extends more distally than the thumb portion, and may have a pre-formed canted or formable distal tip. The canted tip helps to guide the finger into the branch vessel toward the apex of the heart. The thumb of the lead system may also include a preformed curvature angling away from the finger. Electrodes carried by the thumb are preferably oriented so that the electrode surfaces will contact the epicardium when the first finger is fully inserted.
The lead system of the current invention may be delivered by use of a guide catheter. During lead delivery, the lead thumb is maintained in a substantially parallel position with the finger using a stiffening member such as a stylet wire that is advanced within a lumen of the lead. In addition to maintaining the parallel position, the stylet adds stiffness to the lead body so it may be easily pushed through a delivery catheter.
In one embodiment, the lumen for receiving the stylet is formed by one or more insulated sets of conductor cables that are loosely twisted about the stylet and that extend from the proximal end of the lead to the distal end of the thumb where they are connected to one or more electrodes. In this embodiment, the lumen provides only enough clearance for the stylet to be removed from, but not re-inserted within, the lumen. This significantly reduces the lead size.
According to another aspect of the invention, the proximal segment of the lead may includes a conductor coil formed of multiple filars of drawn, silver-cored wire. This wire is wound about insulating tubing that carries the twisted cables and stylet. This coil construction aids in the transfer of torque from the proximal end of the lead. The conductor coil may extend from the proximal end of the lead to the bifurcation of the lead distal tip. At the bifurcation, the coil may transition to a smaller, offset, diameter coil.
A cable made from drawn silver-cored wire may be provided to extend from a point at the bifurcation through the insulated core of the finger. At the distal end of the finger, the cable may be joined to a defibrillator coil electrode that extends over the insulated core and proximally along the finger.
In one embodiment, the bifurcated lead is delivered via a catheter having a distal tip advanced within the coronary sinus to a point near the ostia of the posterior or posterolateral and the great cardiac veins. The lead, in a low profile configuration with the thumb maintained substantially parallel to the finger by the stylet, may be advanced through the catheter. Once the distal tip of the lead is aligned with that of the catheter, the proximal end of the lead may be rotated to orient the canted distal tip of the finger toward the ostium of the posterior vein. The finger may then be advanced into the posterior vein until the tip of the thumb becomes aligned with the tip of the catheter. The stylet may then be withdrawn from the thumb as the lead is pushed forward. The curvature of the thumb will direct the thumb away from the finger and into the ostium of the great cardiac vein. After the elongated members have been fully inserted, the catheter may be withdrawn from the body.
According to one method of using the inventive system, the lead may be employed in conjunction with a standard right ventricular pacing and defibrillator lead to deliver big-ventricular pacing and defibrillator therapy. For example, the thumb portion of the bifurcated lead may provide synchronous pacing pulses delivered in conjunction with pacing pulses provided by the lead implanted in the apex of the right ventricle. Similarly, the finger portion of the bifurcated lead may be used to deliver a cardioversion/defibrillator shock across the cardiac tissue located between the finger portion and the defibrillator electrode that is carried by right ventricular lead.